Using Jboss as7.0.2.Final we have created cluster of four Node N1,N2,N3,N4.

You might consider updating to 7.1.3.Final.

Here N1 is master Node.

How is it master node?

Due to some restriction we are not able to use "Web Managment Interface".

That is a valid requirement, you just want to do this programatically so not via web.

If using "Command Line Interface" we can unregister slave Node N2 from cluster then it is also acceptable.

All the CLI does is invoke the management API, so the result is the same. You just choose which way is more convenient for you (but feeding something to a script seems much easier to me).

What will happen to "HttpSession" and "Infinisan" cache which are hold on slave Node N2 ?

Will they replicated to another node or just destroy ?

What will happen is that with distributed cache, all the copies of the data is replicated on all nodes, so it will pretty much just shutdown. In distributed cache, some of the data will be passed around before shuttind down. In either case, no data is lost of course.

Is there any way to Unregister Node N2 from cluster using "JBoss Application Server management API"?

I dont remember precisely, but i dont think there is a management operation for that in your version. What i suggest though, is that the running webapplication uses that cache. Removing the cache and keeping the appliation running does not seem to be a valid state. Can you just undeploy the running app? This will in return remove the node in the cluster if there is no other service running on that node.